Field of the Invention
The present invention relates to a power semiconductor module which is used in power conversion equipment, such as an inverter and a converter.
The power semiconductor module involves a MOSFET module with a plurality of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) devices built therein, a diode module with a plurality of diode devices built therein, an IGBT module with a plurality of IGBT (Insulated Gate Bipolar Transistor) devices and a plurality of diode devices built therein. Now, the internal structure of the power semiconductor module will be explained in the case of an IGBT module with a plurality of IGBT devices and a plurality of diode devices as semiconductor devices coupled in parallel.
In FIG. 10 is shown a plan view of a semiconductor device section and its vicinities of a conventional IGBT module (hereinbelow, referred to as the module). In FIG. 11 is shown a cross-sectional view of a pair of IGBT device and diode device, and their vicinities in the module. In the module, four IGBT devices and four diode devices are connected in parallel to provide a single module. An IGBT device and a diode device adjacent thereto are reversely connected in parallel so that the emitter of the IGBT device and the anode of the diode device are at the same potential, and the collector of the IGBT device and the cathode of the diode device are at the same potential.
In FIGS. 10 and 11, reference numeral 1 designates a heat dissipating plate made of copper to cool the semiconductor devices, reference numeral 2 designates an aluminum nitride substrate as an insulating substrate, reference numeral 21 designates an electrode pattern provided on each of opposite sides of the aluminum nitride substrate 2, reference numeral 3 designates an IGBT device, and reference numeral 4 designates a diode device. The IGBT device 3 and the diode device 4 are soldered on the electrode pattern 21 side by side. The aluminum nitride substrate 2 is bonded onto the heat dissipating plate 1 by soldering.
Each of the IGBT devices 3 has an emitter electrode 31 provided thereon by patterning, and each of the diode devices 4 has an anode electrode 41 provided thereon by patterning. The emitter electrode is connected to the anode electrode and further to an emitter trunk substrate 7 by aluminum wires 51. The electrode pattern 21 on an aluminum nitride substrate 2, on which an IGBT device 3 and a diode device 4 are soldered, is connected to one of collector trunk substrates 8 by aluminum wires 52. Reference numeral 25 designates a housing, which is made of resin material and is fixed to the heat dissipating plate 1. The collector trunk substrates 8 have electrode patterns provided thereon, and the respective electrode patterns are connected to a module collector electrode 9. To the emitter trunk substrate 7 is connected a module emitter electrode 10. The module emitter electrode 10 and the module collector electrode 9 are connected to a load or the like outside the module housing 25.
In order to control a gate potential for on and off operation of the IGBT devices 3, aluminum wires 53 extend from wiring boards 11 to gate terminals 32 of the IGBT devices 3. Reference numeral 19 designates a module gate electrode, which is connected to the gate terminals 32 of the respective IGBT devices 3 through the wiring boards 11 in the module. Reference numeral 33 designates a current sensing terminal, which is provided on one of the IGBT devices 3, and through which a small current flows in proportion to a current flowing through the emitter electrode 31 of the one IGBT device 3.
In the module with the IGBT devices provided as stated earlier, an overcurrent flows at a value beyond a rated current during operation in some cases, or an excessive current can flow in the module because of short circuit on a load side. When an excessive current flows at a value beyond a rated current in the module, the IGBT devices are heated to be broken, which requires module replacement. In order to prevent the module from being broken due to an overcurrent, it is required that a current flowing through the IGBT devices be detected and that the IGBT devices are turned off immediately before an excessive current flows. A protection circuit is provided in order to prevent the breakage of the IGBT devices, which might cause from the presence of such an overcurrent or on short circuit on a load side.
In FIG. 12 is shown a block diagram of such a protection circuit. Reference numeral 12 designates the module, and reference numeral 13 designates the one IGBT device 3 with the current sensing terminal 33. The current sensing terminal 33 is utilized to detect a primary current flowing through the module emitter electrode 10. The current sensing terminal 33 detects a current flowing through the single IGBT device 13 among the four IGBT devices 3 in the module 12, and the detected current is inputted into a protection circuit 16 against an overcurrent or a short circuit current. Under the action of the protection circuit, a gate voltage control circuit 17 outputs a gate voltage at such a value to turn off the IGBT devices 3 to protect the entire module 2 as required.
The respective IGBT devices 3 have a large number of fine IGBT cells (not shown) connected in parallel therein. The emitter electrode 31 and the current sensing terminal 33 are connected to a large number of IGBT cells in the corresponding IGBT device 13, respectively. The ratio of the number of the IGBT cells connected to the emitter electrode 31 and the number of the IGBT cells connected to the current sensing terminal 33 is set at around 1,000 to 1. Both groups of IGBT cells are separated, and the current that flows through the emitter electrode 31 is measured based on the current that flows through the current sensing terminal 33.
As another prior art, there is a method wherein a resistive element (not shown) is provided at a location in a primary current path and the value of the primary current is detected based on a voltage drop across the resistive element.
A current flowing through the current sensing terminal and the current flowing trough the emitter electrode do not necessarily have the relationship corresponding to the ratio of the numbers of the IGBT cells connected to the respective terminals. The reason is that the IGBT devices are heated during operation to cause a certain temperature distribution on a device surface, and that the temperature of the IGBT cells connected to the current sensing terminal is different from the temperature of the IGBT cells connected to the emitter electrode since the IGBT cells connected to the current sensing terminal is located at a certain position on the device surface. For this reason, the current value detected at the current sensing terminal has not reflected the actual current flowing through the module emitter electrode in accurate fashion in some cases.
In addition, there is provided a problem in that the current flowing through the current sensing terminal varies due to variations in the device production.
In the method to provide a resistive element in a primary current path, the variations in detected values can be minimized since the voltage drop across the resistive element is detected. However, a conventional flat plate shaped resistive element has created a problem in that high-frequency characteristics are not good since the resistive element has large inductance. In the case of a power semiconductor module, such as the IGBT module, a current as large as around 100 A is measured at every IGBT device for instance. In order to reduce power loss caused by the insertion of the resistive element, the resistive element is required to have resistance as low as m.OMEGA.. The flat plate shaped resistive element having such resistance has created a problem in that impedance due to inductance is more dominant than impedance due to resistance in high frequencies from 100 kHz to 1 MHz, and that detection characteristics depend on frequencies.
It is an object of the present invention to provide a power semiconductor module including a current sensing unit capable of detecting a primary current with good precision even in a high frequency region.
According to a first aspect of the present invention, there is provided a power semiconductor module comprising an insulating substrate, a plurality of semiconductor devices provided on the insulating substrate, a plurality of module electrodes provided on the insulating substrate and connected to the semiconductor device, a current sensing unit, the current sensing unit comprising a current sensor including a conductor provided in a primary current path, and the conductor including parallel flat plates so as to have a substantially U-character shape in section, wherein a primary current is detected from a potential difference between inner portions of the conductor.
According to a second aspect of the present invention, the current sensor may be integrally formed with a module electrode.
According to a third aspect of the present invention, the current sensor may be provided on an insulating substrate.
According to a fourth aspect of the present invention, the current sensor may have an insulating film provided between the parallel flat plates in close contact, and one of the parallel flat plates may be provided on the insulating substrate in close contact.
According to a fifth aspect of the present invention, the current sensor may have an insulating film provided between the parallel flat plates in close contact, and one of the parallel flat plates may be provided on a semiconductor device.
According to a sixth aspect of the present invention, the current sensing unit includes two current sensors, and the two current sensors have equal inductance, wherein the primary current is detected from a difference between potential differences at inner portions of the respective current sensors.
According to the first aspect of the present invention, the current sensor can have inductance greatly reduced to offer an advantage that a primary current can be detected with good precision even in a high frequency region since the power semiconductor module comprises the current sensor including the conductor provided in the primary current path, and the conductor including parallel flat plates so as to have a substantially U-character shape in section, wherein the primary current is detected from a potential difference between inner portions of the conductor.
According to the second aspect of the present invention, the power semiconductor module can have a simple structure since the current sensor is integrally formed with the module electrode.
According to the third aspect of the present invention, the power semiconductor module can have a great degree of freedom with respect to the arrangement of the current sensor so as to be versatilely applicable to modules having different structures since the current sensor is provided on the insulating substrate.
According to the fourth aspect of the present invention, the heat that has been generated in the current sensor can be dissipated through the insulating substrate to provide a good heat radiating effect since the current sensor has an insulating film provided between the parallel flat plates in close contact, and since one of the parallel flat plates is provided on the insulating substrate in close contact. When the insulating film is made thin, the current sensor can have inductance further reduced to offer an advantage that a primary current can be detected with good precision even in a higher frequency region.
According to the fifth aspect of the present invention, the current sensor has an insulating film provided between the parallel flat plates in close contact, and one of the parallel flat plates is provided on a semiconductor device. As a result, the insulating film can be made thin to reduce the inductance in the current sensor. The module can be made smaller since there is no additional space for the current sensor.
According to the sixth aspect of the present invention, the two current sensors, which have equal inductance, can be provided so as to be combined to reduce or eliminate the influence of inductance, allowing a primary current to be detected with good precision even in a higher frequency region.